The present invention relates generally to the determining of distances to a reflective surface, and more specifically, to an apparatus and method for determining the extension of a cylinder rod within a cylinder.
Many work machines use hydraulic cylinders for a variety of tasks. Some work machines use them to control the movement and position of a work implement, while other work machines use them to control articulation between sections of the work machine, such as in an articulated truck.
It is frequently helpful to know the precise location of the work implement, or the degree of articulation of the truck, for example. Many work machines use a variety of conventional types of cylinder position sensors to provide this information to an operator, or to an automatic control system to allow for closed loop control of the hydraulic cylinder. One such type of sensor system uses light reflected off one end of a cylinder cavity to determine the position of the cylinder rod. These conventional sensor systems, however, work best when the surface that the light is reflecting off of is perpendicular to the longitudinal axis of the cylinder. This is not always the situation in real world applications.
Many hydraulic cylinders on work machines exert and experience tremendous loads during normal operation. These loads may distort the hydraulic cylinder, such as causing a tilt to the cylinder rod so that it is no longer perpendicular to the longitudinal axis of the cylinder. In these instances, the tilt causes the light to reflect at an unexpected angle, causing error in the determination of the precise amount of extension of the cylinder rod.
The present invention provides a method and apparatus for measuring the distance to a reflective surface. A first light source transmits a first light onto the reflective surface, the first light source being located on a first side of an axis. The reflective surface reflects at least a portion of the light onto a first light-detecting device having a first region operable to receive the reflected first light from the reflective surface. The first light-detecting device transmits a first and second signals as a function of the location of the received first light within the first region. A second light source transmits a second light onto the reflective surface, the second light source being located on a second side of the axis. The reflective surface reflects at least a portion of the second light onto a second light-detecting device having a second region operable to receive the reflected second light from the reflective surface. The second light-detecting device transmits a third and fourth signals as a function of the location of the received light within the second region. A processing device is coupled with the first and second light-detecting devices to respectively receive the first, second, third, and fourth signals. The processing device transmits a position signal indicative of the distance to the reflected surface as a function of the first, second, third, and fourth signals.